For communication and exploration purposes, many structures are placed in outer space. These can be in the form of a space station, a space vehicle or satellites. From the time of deployment to the operating conditions, these structures are subjected to different adverse loadings. These include the stresses and vibrations during launch, extreme fluctuations of temperature from −150° C. to +150° C. (depending on whether the structure is facing the sun or not), impact of space dusts such as atomic oxygens, micro-meteorites, hard vacuum environment, etc. Under these loading conditions cracks and punctures may be formed in these structures. These structures are very expensive to produce and to deploy. It is therefore very important to ensure that their operational life is as long as possible. If cracks are created in these structures, due to their remote locations, it is expensive and impractical to send service people to do repair. If the structure can repair itself after being subjected to loadings that produce cracks the life of the structure can be prolonged.
Due to their light weight, high stiffness and high strength, polymer matrix composite materials have been used to make many parts of space structures, aircraft, as well as a wide range of high performance products including tennis racquets and other sporting goods. While in aircraft, the operating range may vary roughly from −60° C. to +50° C., in other applications for high performance composite materials, the operating temperature range may be less vast. Polymer composite materials consist mainly of strong and hard fibers such as carbon, glass and aramid fibers, and resin matrix such as epoxy resins. Fibers are resistant and may not break easily. However the resin matrix may crack more easily.
There has been development of self-healing of epoxy matrix resin for general purpose applications. This has been described in U.S. Pat. No. 6,518,330 to White et al and U.S. Pat. No. 6,858,659 to White et al. These patents teach a material that is self-healed by thermal treatment above the normal operating temperature of the material, namely the material is taken out of its operating environment, raised to a temperature above 33° C. at which the monomer flows into any cracks and polymerizes, and then cooled down to the normal operating temperature.
Another approach for healing of polymeric resins is to incorporate hollow fibers into the matrix resin. (Semprimoschnig C., “Enabling self-healing capability—a small step to bio-mimetic materials”, Materials Report number 4476, European Space Agency, Jan. 12, 2006). In this approach, hollow glass fibers are embedded in the polymer matrix materials. Semprimoschnig C. et al., used a two-part healing materials infused in separate hollow fibers. When a crack occurs, it breaks the hollow fibers, and the two-part healing materials flow out to fill the cavity of the crack. The reaction requires external heating (2 hours at 100° C.) to enable a complete curing. Also the healing efficiency is not high.